The invention relates to a process and apparatus for the preparation of mortar, such as jointing mortar.
It is known that ready-made mortars can be prepared in a mortar plant where the aggregate, binding agents and water are weighed out for a definite batch and then conducted to a mixing chamber. The product is referred to as wet mortar to which a retarder can be added in order to keep the mortar workable for a longer period. The wet mortar is conveyed to the building site by trucks having rotating (mixing) drums mounted on them.
A system for manufacturing ready-made mortars in a mortar plant is disclosed by Tobolov et al, U.S. Pat. No. 3,451,659. Tobolov et al disclose a plant for mixing sand with a hardener in which the rate of sand feed is controlled by a conveyor belt and the rate of hardener feed is controlled by a screw feeder. After being mixed, a liquid is then added to the mixture. Thus the rates of sand and hardener feed rates are controlled to achieve the desired proportions of each in the mixture. Apparently, Tobolov et al's finished product is wet mortar which must still be conveyed to building sites by trucks equipped with rotating (mixing) drums.
It is also known that dried and premixed mortars can be prepared in a special drying and mixing plant, whereupon the dry mortars are transported to the building site by bulk lorry. At the building site the dry mortar is dumped into a storage bunker positioned over a mixing device for mixing the dry mortar with water so as to obtain a workable mortar.
The known processes and apparatus have the following drawbacks:
The aggregate must be predried in order to obviate partial hardening with the previously mixed binding agent, a rather costly step in view of the expenditure of energy.
As the aggregate is not completely dry in actual practice, the dry mortar has only limited keeping qualities.
The completely weighed-out batch from the storage bunkers must invariably be mixed with water, which leads to waste of mortar not needed for immediate use.
It is further known to use separate containers for containing the binder and aggregate separately. These containers are then mounted onto trucks and transported to building sites where the binder and aggregate are mixed and used. Such systems are disclosed, for example, in U.S. Pat. Nos. 3,048,377 to Braitsch and 4,189,237 to Bake. Since trucks making deliveries of binder and aggregate may be delivering to more than one building site, and since the requirement at each building site may differ, it is desirable for the containers on the trucks to be capable of dispensing different quantities of binder and aggregate at each site. While Bake did disclose that the entire stock of binder and aggregate on the truck might be stored in a number of containers so that only some of the containers would be emptied at each site, the entire contents of one or more containers must be dispensed at a time. Thus if the actual amount of materials desired on site turned out to be different from those contained in any one of the containers, the excess amounts dispensed would be wasted.
For many construction tasks, it is desirable to have an inexpensive supply of moderate but variable amounts of high quality mortar continually over an extended time period. For such tasks, none of the above described systems appear to be entirely satisfactory. It is therefore desirable to provide an economical and flexible system which is capable of fulfilling such needs.